Yes, of course. Did remember its not fork(), but some other *fork() and couldn't remember the name. But just the kind of thing it does. Its also not exec(), but probably execvp() or execvpe() or something like that.

It's important to note because vfork is exactly what makes it close to posix_spawn, as opposed to regular fork.

When using vfork() what are you allowed to do? Can you even do IO redirection (piping)? The man page says:

> ... the behavior is undefined if the process created by vfork() either modifies any data other than a variable of type pid_t used to store the return value from vfork() ...

But the time between fork and exec is exactly where you do a lot of setup, like IO redirection, dropping privileges, setuid(), setting a signal mask (nohup) etc. and I don't think you can do that without setting any variables. You certainly write to the stack when calling a function.

If you can't do these things you can't really use it to implement posix_spawn(). I guess it could use vfork() in the case no actions are required, but only then.